1. Field of the invention
This invention relates to a driving circuit for a liquid crystal display apparatus, and more particularly to a driving circuit for a liquid crystal display apparatus in which thin film transistors are used as switching elements.
2. Description of the prior art
FIG. 6 shows a driving circuit for driving an active matrix type LCD apparatus 1 in which thin film transistors (TFTS) are arranged as switching elements in a matrix form. The driving circuit shown in FIG. 6 comprises a source driver 2, a data driver 3, a controller 4, and a polarity-inverting circuit 5. When a DC voltage is applied to the liquid crystal in the LCD apparatus 1, electrochemical reaction occurs in the liquid crystal, thereby deteriorating the liquid crystal. In order to prevent such deterioration from occurring, the driving circuit is provided with the polarity-inverting circuit 5 so that the LCD apparatus 1 is AC-driven.
The polarity-inverting circuit 5 generally comprises an amplifier, an inverter which inverts the polarity of the output of the amplifier, and a switching circuit which alternatingly selects either of the outputs of the amplifier and inverter to output the selected output. The polarity-inverting circuit 5 converts input video signals into polarity-inverted signals (AC signals). FIG. 7 shows gray scale video signals. For example, the polarity-inverting circuit 5 converts the video signals of FIG. 7 into polarity-inverted signals shown in FIG. 8.
When the LCD apparatus I displays the same time for a long period of time, the pattern is "memorized" in the liquid crystal, with the result in that some extent of time is required to completely distinguish this memorized pattern. Even when another pattern is to be displayed, therefore, this memorized pattern also appears as a residual image on the apparatus 1 (i.e., the residual image phenomenon occurs). This residual image phenomenon greatly impairs the image quality.